The accurate measurement of microscopic objects whose sizes are in the range of one to fifty .mu.m requires that the object be moved slowly under a reference line or an extremely fine cross air in the measuring instrument. Displacements of the object are usually measured with the use of an interferometer, an encoder or a linear variable differential transformer. In order to be useful, the stage on which the object is placed must be capable of linearly positioning objects over the required range with resolutions of 0.001 .mu.m or less and with a motion that is as free as possible of vibration, pitch, roll and yaw. In addition, the stage's design should allow the stage to be remotely activated and thus capable of being isolated from external vibrations and other environmental disturbances.
Devices of the prior art which have been used for micropositioning stages have frequently employed mechanical bearings and screws to permit the required movement of the object being studied. Such devices have however suffered from problems of screw backlash and the need for lubricants which can present problems when cryogenic temperatures or vacuums required for electron microscopy are used.
In addition, systems of the prior art for micropositioning objects where movement of the object along two axial directions is contemplated have involved the stacking of one stage of top of the other in a vertical arrangement. This procedure, while permitting biaxial orientation and displacement of the object also results in deviation in accordance with the "Abbe" principle which has been summarized in the statement:
"The placement measuring system should be in line with the functional point whose displacement is to be measured. If this is not possible, either the slideways that transfer the displacement must be free of angular motion or angular motion data must be used to calculate the consequences of the offset." J. B. Bryan, "The Abbe Principle Revisited--An Updated Interpretation", Lawrence Livermore Laboratory, May 14, 1979.
Accordingly, it is an object of the present invention to provide a monolithic micropositioning stage for biaxial movement of an object which avoids the above-noted problems associated with using screw drives, lubricants and bearings.
It is a further object of the present invention to provide a micropositioning device which allows biaxial movement of the object being studied in a single plane.
Yet a further object of the present invention is to provide a micropositioning device for movement of the objective in two directions which avoids the "Abbe" deviation heretofore encountered in systems where multiple stages are stacked vertically upon one another.
Yet a further object of the present invention is to provide a micropositioning system which avoids the need for sliding or rolling of members and which require lubrication and may produce friction and bearing noise.
Still another object of the invention is to provide a fast, electrically controlled response time for linear movement of the object which is proportional to applied voltage.